This invention relates to an alkylated (i.e., C.sub.1 -C.sub.3) derivative of a known compound and a method for producing it. The known compound is an oxo-piperazinyl triazine ("PIP-T" for brevity) which consists of a triazine ring having three polysubstituted piperazine-2-one ("PSP") substituents, each distally spaced apart from each C atom of the triazine ring by a polyalkyleneamine bridge. The PSP substituent is so termed because the 3- and 5- C atoms of the diazacyclohexane ring are each disubstituted with methyl groups.
As will immediately be apparent, a PIP-T is a large molecule. It is known that when this molecule is present in an organic material in an amount sufficient for the purpose at hand, there results a thermooxidatively stabilized composition, resistant to degradation by UV light. The general structure of a PIP-T is disclosed in U.S. Pat. No. 4,480,092 to Lai, et al. (class 544/subclass 113), the disclosure of which is incorporated by reference thereto as if fully set forth herein. PSP compounds are taught in U.S. Pat. Nos. 4,190,571; 4,292,240; and 4,298,737 inter alia. Like PIP-Ts, the 3,3,5,5-tetra-substituted PSPs provide excellent light stabilization, but have substantially lower thermooxidative stabilization than PIP-Ts.
As one skilled in the art will readily appreciate, the stabilization properties of both PSPs and PIP-Ts are attributable to the hindered N.sup.4 atom in each PSP, steric hindrance being the result of having di-substituted 3- and 5- C atoms. The superior overall stabilization properties of a PIP-T substituted with three 3,3,5-5-tetraalkyl-substituted PSPs is attributable to the triazine ring and the bulky configuration of this specific PIP-T of this invention. All references to PSPs hereafter are to the 3,3,5-5-tetraalkyl-substituted piperazinone moieties; and reference to "the PIP-T" refers to a triazine ring substituted with three such PSPs, each distally spaced apart from the triazine ring by an ethyleneamine bridge and connected to the ring by a tertiary N atom.
To the extent that bulk contributed to stabilization, the obvious way to increase the overall bulk of the PIP-T is to provide bulky substituents at the 3- and 5- positions of the PSP ring, and at the N atom in the ethyleneamine bridge of an '092 PIP-T. Though this bridge on each of the three PSPs connected to the triazine ring adds to the bulk of the molecule, each bridge provides its connected PSP with requisite mobility sufficient to permit alkylation of the hindered N.sup.4 atom with a methyl group, an ethyl group, or a propyl group. Still other suggested substituents are those at the 6-position of the diazacyclohexane ring and the N.sup.4 position, which substituents are suggested by Conetta, et al. in U.S. Pat. No. 4,753,979. There was no particular reason for anyone to provide any substituent at the N.sup.4 atom of the PSP, and any inclination to do so would be dispelled by the knowledge that the steric hindrance at the N.sup.4 atom militated against making such a substitution.
Therefore there was no motivation to make any substitution at the N.sup.4 atom. It was not foreseeable that a PIP-T that was alkylated with a methyl group, ethyl group, or propyl group, preferably with a methyl group, would have a unique and distinctive stabilization effect on the susceptibility of specific synthetic resinous materials, quite different from the effect obtained by the known unmethylated compound, itself an excellent stabilizer.
Having successfully alkylated the N.sup.4 atom specifically with a methyl group, it was discovered quite fortuitously, that the methyl substituent in the PIP-T (hence "methylated PIP-T") was unexpectedly effective as a stabilizer for polyacetal resins. Since providing a methyl (or ethyl or propyl) substituent on the ring N atom of a diazacyclohexane is typically a routine task, this would appear to present little difficulty. However, the methylation (or ethylation or propylation) must be successful on each hindered N.sup.4 atom of each of the three PSPs, yet not occur at any other location in the PIP-T. It was not apparent how this could be done.
Moreover, as will readily be appreciated, the stabilization effect sought will only be realized if a mass of essentially pure methylated (or ethylated or propylated) PIP-T is introduced into and homogeneously dispersed into a natural or synthetic resinous material which is to be stabilized. By "by essentially pure" we refer to a hindered amine light stabilizer (HALS) which is at least 95% pure and has less than 500 ppm (parts per million) ash, preferably less than 100 ppm being the oxides of metal impurities which are critical in determining degradation of color. By "stabilization effect" we refer specifically to the effect on the material which must be protected against degradation by heat and light, especially ultraviolet (UV) light. For polyacetal compositions containing the methylated (or ethylated or propylated) PIP-T, such an effect can be determined by testing the discoloration and weight loss that occurs, if any does occur, in such compositions upon exposure to ultraviolet light and by further testing the thermal stability of such compositions.
Because the PSP is to be connected to the triazine ring through the N atom of the amine group in the bridge, thus forming the PIP-T, the PSP must necessarily be unsubstituted at the N.sup.4 atom before making the connection. The obvious reason is that any substitution made at the N.sup.4 atom before connecting the PSP to the triazine ring, would also be made at the N atom of the amino group, thus frustrating the connection to the triazine ring.
Since the function of the substituents on the ring and the bridge are now found to be clearly related to the effectiveness of the PIP-T as a stabilizer, it became imperative that any substitution of the N.sup.4 atom be made after the connection of the PSP to the triazine ring.
The problem of alkylating the hindered N.sup.4 atom in a diazacycloalkane molecule was solved in a straightforward manner in U.S. Pat. No. 4,190,571 in which a method of propylating the N.sup.4 atom is disclosed. The 3,3,5,5-tetramethyl substituted diazepin-2-one was heated with 1-chloropropane. Thus, it was known that in a 3,3,5,5-tetramethyl substituted diazacycloalkane ring, the N.sup.4 atom was not so highly hindered as to preclude "fitting" a propyl group into the space defined by the adjacent substituents on the 3- and 5-C atoms. As one would expect, having three polysubstituted diazacyclohexane groups attached to a single triazine ring would increase the difficulty of "finding" the N.sup.4 atom. But connecting the PSPs to the triazine ring through the terminal primary amine group of the bridge would not be permitted because the H atom on the amine N atom connecting the PSP to the triazine ring, would also be methylated (or ethylated or propylated).
The problem of methylating a hindered N atom in a heterocyclic nitrogen compound has been addressed in a 2,2,6,6-tetrasubstituted piperidyl compound connected to plural triazine rings in U.S. Pat. No. 4,816,507 to Cantatore, et al. (Class 524/sub 100). Each triazine ring, in turn, is directly connected to the N atom of an acyclic polyamine and only two polysubstituted piperidyl substituents can be connected to each triazine ring. Further, each polysubstituted piperidyl substituent is directly connected to the triazine ring through a single tertiary N atom.
The difficulty of producing the methylated compound of the '507 patent is learned by carrying out the Eschweiler-Clark synthesis procedure described in Example 1 thereof. When the piperidyltriazine compound is methylated, a mixture of methylated compounds results. The major amount is a compound containing 8 pentamethylated piperidyl groups, and a 9th methyl group on either the terminal N.sup.I or N.sup.IV atoms, and lesser amounts of compounds are formed in which neither terminal and atom or both of them are methylated. There is no suggestion of how the methylated compounds with the pentamethylated groups might be separated from unreacted starting material and other compounds in the reaction mass, and we know of no way to do so.
Though the degree of difficulty involved in making a substitution is not a criterion for unobviousness unless the compound cannot be made, the degree of difficulty becomes of critical importance if a mass of essentially pure crystals are to be made and there is no known method for making it. In the specific instance of the methylated PIP-T, if the compound recovered is less than 90% pure, the impurities and by-products of the reaction function as prodegradants in the resin substrate to be stabilized. Further, if the conversion to the methylated PIP-T is less than 90%, purification of the methylated PIP-T in the mixture is impractical.
PSPs have been substituted at the N.sup.4 position in Japan Public Patent Disclosure Bulletin No. JP 63-8711 but there is no indication of how substitutions may have been made, nor how a mass of such N.sup.4 -substituted compound was recovered from the reaction mass.
This invention is specifically directed to the alkylated PIP-T in which each of the three N.sup.4 atoms of each PSP are necessarily alkylated, said alkylation being done with a methyl group, an ethyl group, or a propyl group, and each N atom connecting the PSP to the triazine ring is the terminal tertiary N atom of an ethyleneamine bridge; to a stabilizer product which is an essentially pure mass of the PIP-T alkylated with a methyl group, an ethyl group, or a propyl group; and, to a process of making the product with a conversion of at least 90% by weight of the starting PIP-T.